Paging receivers are battery powered devices which are utilized by subscribers who want to be accessible without being tied to a known location. Typically, in order to meet consumer demand, paging receivers are relatively small and light in weight so that a subscriber can carry a paging receiver without becoming fatigued. Therefore, both the receiver circuitry and the battery for powering the circuitry must be situated in a limited amount of space.
Further consumer demands dictate that the battery life of the battery powering the paging receiver should be long enough that the subscriber is not often inconvenienced by having to replace the battery. In other words, the battery should have a relatively high capacity. It follows, then, that small, high capacity batteries for powering paging receivers typically provide low voltages, i.e., voltages on the order of 1-1.5 volts. In many cases, however, circuitry, such as controllers and microprocessors, included within a paging receiver require higher voltages. As a result, voltage multiplying circuitry is included within the paging receiver for boosting the battery voltage to the higher voltage required by selected circuits within the paging receiver.
Conventionally, voltage multiplying circuitry is coupled to the battery by a switch which is rapidly opened and closed to charge circuit elements of the voltage multiplying circuitry with a current from the battery, thereby generating a higher output voltage for use by the higher voltage paging circuits. This switching unfortunately results in the generation of high frequency harmonic signals which can desensitize the paging receiver. This interference can be so severe that the paging receiver erroneously receives or entirely misses weaker radio frequency signals. Additionally, the high frequency harmonic signals can mix with the radio frequency signals detected by the antenna to produce unwanted signals, i.e., spurious responses, in the intermediate frequency range of the receiver.
Thus, what is needed is a method and apparatus for controlling radio frequency interference generated by voltage multiplying circuitry included in a paging receiver.